Wearables: The pros and cons of health tracking

"Is that a Series 4?" a cardiologist asked me, with evident interest. In the course of a conversation last year, he'd noticed I was wearing an Apple Watch.

No, I confessed; I’d opted for the cheaper Series 3. He looked disappointed, noting that alas, my model lacked the ECG function. This takes an accurate 30-second measurement of heart rate and rhythm, as opposed to the more basic heart monitoring of my model and most other fitness wearables.

Taking an ECG, or electrocardiogram, used to involve gluing numerous electrodes to the skin of the chest and back (12 being the standard) in a medical setting, or while wearing a portable device.

Now, most fitness trackers give a sufficient heart reading, though not of medical standard, for workouts and tracking heart health.

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But the Apple Watch, and some others, go further. Newer releases, with better sensors, have approval from regulatory bodies such as the US FDA (Food and Drug Administration) as a lower-grade medical device. The watch also has received the EU’s CE mark for health and medical standards compliance.

In a study, Apple’s ECG app showed a 98.3 per cent sensitivity in identifying atrial fibrillation, one of the most common heart arrhythmias, and a potentially dangerous one – if you have atrial fibrillation (AFib), you need to see a cardiologist. It also was 99 per cent accurate in classifying sinus (normal) rhythm in recordings, when compared with a 12-lead ECG.

A basic one-lead recording won’t be able to identify a heart murmur, a heart attack, or a stroke, or other specific arrhythmias. But, as many cardiologists have noted, these devices can be lifesavers. AFib and other irregular beats don’t always display obvious symptoms.

Other devices can give even more detail. For example, medically certified Kardia monitors, barely larger than a credit card and which snap into a holder on a mobile phone, can take one- or six-lead readings. These (as with the Apple Watch) will produce a PDF of the reading and email it to your doctor. The cardiologist I chatted to has patients using one or the other, though the watch is handier as it doesn’t require the user to fiddle with launching a separate phone app or positioning the device. You just touch the Apple Watch’s “crown”, the side dial protrusion.

The downsides

Wearables have downsides. Health tracking easily becomes obsessive, and much of what these devices track – heart rhythms and pulse, sleep, blood oxygen – falls into the realm of fuzzy inaccuracy (due to the hardware, or the software algorithms) or unknown unknowns, as what’s “normal” isn’t fully understood.

Wearables are handy for tracking activity and fitness, but even the best do so at varying levels of accuracy

Anyone with a wrist wearable has likely seen odd readings, likely due to the limitations of the device (if your wrist is too sweaty, the band is too loose or tight, or arm movements are too erratic, as with much exercise beyond walking or running). Apple Watch’s new oxygen monitor function is not medically certified, and can give inaccurate readings (I’ve found it mediocre).

Device and app algorithms – proprietary, of course, so we have no idea how they work or the research on which they are based – have been the target of expert criticism, too. Sleep analysis algorithms in apps that use data from fitness wearables irritate many sleep specialists, who say they give fanciful interpretations of sleep phases and, ironically, fuel sleep-affecting worry. I’ve seen exactly that on internet forums where some had wearables indicating they were walking zombies, barely getting deep sleep, causing full-on health panic.

As for the unknown unknowns: experts say no one fully knows what “normal” variations may be for, say, heart rhythms or sleep. Only a few years ago, some arrhythmias now understood as benign variations were considered a risk requiring medical management.

But now that we can constantly monitor ourselves, all variations can stick out and contribute to data obsession (in the search for “normal”) and health anxiety. With sleep tracking, such data dependence even has a term now: orthosomnia. All of this irks many GPs and specialists because wearables may generate unneeded medical visits.

Then, there's valid concern about what happens to the health data generated from seemingly innocuous wearables. Health apps typically require EU users to permit data to be sent to the US, to be utilised under less stringent privacy protections, or be made available for vague "research". How might your health data be used by third parties, now and in the future? Google's acquisition of wearables maker Fitbit – approved by the EU – alarms privacy advocates for exactly these reasons.

All are important considerations. Wearables are handy for tracking activity and fitness, but even the best do so at varying levels of accuracy. They can capture genuinely concerning health conditions, and save lives. They also can provide health professionals with important monitoring information. But users easily misunderstand and overestimate what the devices do, how they might best be used, and where personal data goes.

For more detail, the August edition of Which? consumer magazine contains a good guide to these basic issues.